Oral Sulfate solution (Suprep) in day before and split-dose regimens In the OSS arm: between 17:00 and 18:00 hours on the day before colonoscopy, subjects were instructed to pour one 180-ml bottle of the study medication into a provided 480-ml mixing cup and fill it with water and then drink the entire volume, followed by two additional 480 ml of water. At approximately 6:00 a.m. on the following morning, the subjects took the second dose of OSS by same formulation protocol.

4L PEG solution in day before and split-dose regimens In the 4L PEG arm: subjects had the first 2L between 18:00 and 19:00 hours (250mL every 15 minutes) in the evening before the colonoscopy. And the second 2L was given between 07:00 and 08:00 on the day of colonoscopy.

Oral Sulfate solution (Suprep) in day before and split-dose regimens In the OSS arm: between 17:00 and 18:00 hours on the day before colonoscopy, subjects were instructed to pour one 180-ml bottle of the study medication into a provided 480-ml mixing cup and fill it with water and then drink the entire volume, followed by two additional 480 ml of water. At approximately 6:00 a.m. on the following morning, the subjects took the second dose of OSS by same formulation protocol.

The boston bowel preparation scale The BBPS uses a 10-point (0-9) summation scale assessing bowel preparation quality, by a 3 point scoring system of 0 to 3 in 3 segments of the colon (right colon, transverse colon, and left colon), where 0 = ''unprepared colon with mucosa not seen because of solid stool,'' 1 = ''portion of colonic mucosa of the segment seen, but other areas not well seen due to staining, residual stool, and/or opaque liquid,'' 2 = ''minor amount of residual staining, stool, and/or opaque liquid, but colonic mucosa of the segment seen well,'' and 3 = ''entire colonic mucosa seen well with no residual staining, stool or opaque liquid.'' An adequate bowel preparation was defined by a total BBPS score ≥ 6 with all segment scores ≥ 2, and excellent cleansing was considered as a score of > 7.

Proportion of adverse events. Adverse events recorded on the questionnaires included nausea, vomiting, abdominal pain, bloating, sleep disturbance, numbness, weakness/faint feeling, fecal incontinence, and thirsty.

Blood samples were taken at the screening visit and the day of the procedure and were analysed for serum electrolytes (sodium, potassium, chloride, calcium, phosphate and magnesium), blood urea nitrogen (BUN), creatinine and glomerular filtration rate (GFR). Incident kidney injury was defined as a 25% increase in serum creatinine levels or longitudinal significant change in estimated glomerular filtration rate.